1. Field of the Invention
The invention relates to an electrical actuator comprising a first actuator body, a second actuator body which is pivotable with respect to the first actuator body through an angle of rotation about an axis of rotation, electrical energizing means for exerting an electromagnetic torque on the second actuator body, and an electrical control unit for controlling the angle of rotation of the second actuator body, said control unit comprising an electrical input for receiving an electrical signal corresponding to a required angle of rotation of the second actuator body and an electrical output for supplying an electrical signal corresponding to a required electrical current through the energizing means.
The invention further relates to a throttle device for use in an air inlet of an internal-combustion engine, which throttle device comprises a throttle-valve housing, an air passage which is connectable to the air inlet, a throttle-valve which is journalled in the throttle-valve housing so as to be pivotable in the air passage, and an electrical actuator for pivoting the throttle-valve.
2. Description of the Prior Art
An electrical actuator of the kind mentioned in the opening paragraph is disclosed in chapter 15.2 entitled "Linear Position Control" of the book "Control of Electrical Drives" by W. Leonhard, ISBN 3-540-13650-9 Springer-Verlag Berlin Heidelberg New York Tokyo. The control unit of the known actuator has a so-called cascade control structure comprising a system of several superimposed control loops for the electromagnetic torque, the angular acceleration, the speed of rotation and the angle of rotation of the actuator. The control loop for the electromagnetic torque comprises a control member with an electrical input for receiving an electrical signal corresponding to a required angular acceleration and an electrical output for supplying the electrical signal corresponding to the required electrical current through the energizing means. The cascade control structure provides a natural control sequence which corresponds to the structure and operation of the actuator. As a result, the control unit has a transparent structure and can be designed and optimized step by step.
A drawback of the known actuator is that the response of the control unit of the known actuator to alterations of the signal corresponding to the required angle of rotation is relatively slow if the dependence of the electromagnetic, magnetostatic or mechanical characteristics of the actuator on the angle of rotation of the second actuator or on the current through the energizing means is strongly non-linear. Due to the non-linearity of said characteristics, the number of iterative calculations which have to be made by the control unit before a required angle of rotation is achieved is relatively high.